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PROGRAM TEST
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IMPLICIT NONE
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C
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INTEGER LDB, LDIWRK, LDWORK, N, NRHS
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PARAMETER (N = 5)
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PARAMETER (LDB = N)
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PARAMETER (LDIWRK = N)
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PARAMETER (LDWORK = 2 * N)
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PARAMETER (NRHS = 1)
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C
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DOUBLE PRECISION ANORM, B(LDB,NRHS), DIAG(N), DLOWER(N-1)
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DOUBLE PRECISION DUP1(N-1), DUP2(N-2), RCOND, WORK(LDWORK)
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INTEGER ICOL, INFO, IPIVOT(N), IROW, IWORK(LDIWRK)
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C
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EXTERNAL DGTCON, DGTTRF, DGTTRS
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INTRINSIC ABS, MAX
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C
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C Initialize the arrays DLOWER, DIAG, and DUP1 to store
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C the first subdiagonal, the diagonal, and the first
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C superdiagonal of the coefficient matrix A shown below.
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C Initialize the array B to store the right hand side
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C matrix b shown below.
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C
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C -3 1 6
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C 1 -2 1 12
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C A = 1 -2 1 b = 18
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C 1 -2 1 12
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C 1 -1 6
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C
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DATA DLOWER / 1.0D0, 1.0D0, 1.0D0, 1.0D0 /
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DATA DIAG / -3.0D0, -2.0D0, -2.0D0, -2.0D0, -1.0D0 /
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DATA DUP1 / 1.0D0, 1.0D0, 1.0D0, 1.0D0 /
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DATA B / 6.0D0, 1.2D1, 1.8D1, 1.2D1, 6.0D0 /
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C
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C Print the initial value of A.
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C
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PRINT 1000
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DO 100, IROW = 1, N
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PRINT 1010, (0.0D0, ICOL = 1, IROW - 2),
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$ (DLOWER(ICOL + 1), ICOL = ABS(IROW - 2),
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$ IROW - 2), DIAG(IROW),
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$ (DUP1(IROW), ICOL = 1, MIN(1, N - IROW)),
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$ (0.0D0, ICOL = IROW + 2, N)
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100 CONTINUE
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PRINT 1020
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PRINT 1030, B
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C
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C LU factor A.
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C
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CALL DGTTRF (N, DLOWER, DIAG, DUP1, DUP2, IPIVOT, INFO)
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IF (INFO .NE. 0) THEN
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PRINT 1040, INFO
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STOP 1
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END IF
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ANORM = 4.0D0
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C
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C Estimate and print the condition number of A.
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C
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CALL DGTCON ('ONE-NORM', N, DLOWER, DIAG, DUP1, DUP2,
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$ IPIVOT, ANORM, RCOND, WORK, IWORK, INFO)
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IF (INFO .NE. 0) THEN
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PRINT 1050, ABS (INFO)
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STOP 2
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END IF
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PRINT 1060, 1.0D0 / RCOND
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C
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C Solve the system and print the solution.
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C
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CALL DGTTRS ('NO TRANSPOSE A', N, NRHS, DLOWER, DIAG, DUP1,
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$ DUP2, IPIVOT, B, LDB, INFO)
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IF (INFO .NE. 0) THEN
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PRINT 1070, INFO
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STOP 3
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END IF
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PRINT 1080
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PRINT 1030, B
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C
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1000 FORMAT (1X, 'A:')
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1010 FORMAT (5(3X, F5.2))
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1020 FORMAT (/1X, 'b:')
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1030 FORMAT (1X, F8.2)
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1040 FORMAT (1X, 'Error factoring A, INFO = ', I5)
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1050 FORMAT (1X, 'Illegal argument to DGTCON, argument #', I2)
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1060 FORMAT (/1X, 'Estimated condition number of A: ', F6.2)
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1070 FORMAT (1X, 'Error solving Ax=b, INFO = ', I5)
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1080 FORMAT (/1X, 'x:')
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C
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END
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